Electromagnetic device



Patented Sept. 26, l 1

2,359,224 mscraomcna'rrc nevica Kornelis Swier Knol and Maximiliaan Julius Otto Strutt, Eindhoven, Netherlands; vested in the Alien Property Custodian Application April 12, 1941, Serial No. 388,250 In the Netherlands April 29, 1940 2 claims. '(ci. ris-i5) This invention relates to an electro-magnetic device such as a coil or a conductor and has for its purpose to raise the induetance of such a device at frequencies exceeding 109 cycles/sec. and more particularly by making use of ferromagnetcmaterial According to the invention this purpose is attained by making use of layers of coherent ferro-magnetic particles applied on to a support.

When measuring the alternating current resistance of thin solid iron wires at high frequencies the magnetic permeability can be calculated from the resistance values obtained. Many investigators ascertained by means of such resistance measurements that the permeability at room temperature at frequencies of several cycles/sec. up to about cycles/sec. is constant. Above 108 cycles/sec., however, the permeability exhibits a rapid drop of the initial value (for instance 100) to unity. Consequently it is unfeaslble to utilise thin iron wires for raising the inductance, for instance of coils designed for frequencies above say 109 cycles/sec.

particles of which they are formed stick together4 so that these layers have a metallic appearance. In a suitable method of manufacture a solution of 50 parts by weight of FeCla; 50 parts'by weight of CaCl: and '75 parts by weight of distilled Water was made to boil and subsequently filtered. After that the electrolysis was effected at a temperature of the bath of about 90 C., a cylindrically curved piece of iron plate of pure iron constituting the anode and a constantan wire, for instance, serving as a cathode. The current density amounted to about 30 ma./cm.2 on the last-mentioned wire. be coated was previously treated with a degreasing agent, pickled in diluted hydrochloric acid, Washed in distilled water and immediately subjected to the electrolytic treatment. If this method is carried out carefully and as pure as possiblev solutions are used dense coherent iron layers are obtained which under a metal microscope (with a magnication of about 100) I exhibit a metallic appearance which is only The constanten wire toslightly different from the surface of solid iron Wires. By resistance measurements the specific resistance and its dependency with respect to temperature couldhe determined frcml the thickness of the layer also determined microscopically. In this way. also, perfectly coherent layers of pure iron are found. The thickness of the layer must exceed 1.5 microns.

Iron layers can be precipitated electrolytically' also on iron wires, it being advisable that the iron wires to be coated should previously be The curve s in Fig. 2 indicates the initiall permeability ,u in accordance with the frequency f of an iron layer made in the manner referred to above. Therefrom it appears that the initial l permeability up to 109 cycles/sec. is substantial--y 1y Iconstant and then gradually decreases, but at 101 cycles/sec. still has the very high value of about 80.

The wires coated with a .layer of precipitated iron particles have an increased induetance and may, for instance, be used in amplifying tubes for short waves in which `it is sometimes desirable to increase the inductance of the supply conductors for one or more electrodesof these tubes.

Furthermore layers precipitated on/wires or plates may be formed into cores for coils used at frequencies above 109 cycles/sec.

It is to be noted that the layersl may be made not only of iron, but also of other ferro-magnetic materials such as nickel, iron-nickel and so on.

Instead of applying. the layers electrolytically they may also be provided on their supports y by cathode disintegration or electrophoresis.

What we claim is: f

1. An electrical conductorcomprising a metallic support, a layer of dense coherent ferromagnetic particles on said-support formed by electrolysis at current desities of approximately 30 mia/cm?, said layer having a thicmess in excess of 1.5 microns and a permeability of substantially for a range of frequencies from zero up to approximately 10s cycles/second.

constantan wire 'provided with an outer coating of coherent particles of ferro-magnetic material formed by electrolysis at current densities of appmximately 30 ma./cm., said coating having a thickness in excess of 1.5 microns, and said coating having apermeability of approximately 100 over a range of frequencies from zero up to apvproximately 10 cycles/second and which thereafter gradually decreases to about 80 to ap- 'Proximately i0" cycles/second.

KORNELIS SWIER KNOL. MAXDILIAAN JULIUS OTTO SI'RU'I'I. 

